Abstract
Alloy 600 is used extensively in nuclear steam generators and in reactor internal components such as vessel head penetrations. Here, a new model for intergranular stress corrosion cracking (IGSCC) of Alloy 600 is presented. In the Selective Dissolution-Vacancy-Creep (SDVC) model for IGSCC of Alloy 600 the rate determining step is the generation of cation vacancies by selective dissolution of metal cations through the existing passive film at the crack tip. The vacancies migrate towards the location of the maximum stress concentration enhancing and localizing creep. Crack advance occurs by formation of a shear band at the crack tip, further accumulation of vacancies in the dislocation free volume of the shear band and final breakdown of bonds between atoms as the vacancy concentration exceeds a critical value. Passivation of the freshly formed bare surfaces enhances generation of new cation vacancies, which then migrate towards the new location of the maximum stress concentration. After reaching a critical vacancy concentration in the shear band ahead of the new crack tip, cracking can proceed. In this paper the validity of the SDVC model is discussed based on experimental and literature data. It is shown that the pH and temperature dependencies of IGSCC crack growth rate and the effects of zinc injection, hydrogen overpressure and grain boundary carbide distribution on the IGSCC crack growth rate of Alloy 600 are qualitatively in accordance with the model. The model also qualitatively predicts the effect of electrochemical potential on IGSCC crack growth rate. Based on the model a valid explanation is given for the experimentally observed IGSCC cracking at cathodic potentials.
| Original language | English |
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| Title of host publication | Seventh International Symposium on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors |
| Subtitle of host publication | Proceedings and symposium discussions |
| Editors | Geoffrey Airey, Peter Andresen, James Brown |
| Place of Publication | Houston |
| Publisher | National Association of Corrosion Engineers (NACE) |
| Pages | 841-854 |
| ISBN (Print) | 978-1-877914-95-9 |
| Publication status | Published - 1995 |
| MoE publication type | A4 Article in a conference publication |
| Event | 7th International Symposium on Environmental Degradation of Materials in Nuclear Power Systems: Water Reactors - Breckenridge, United States Duration: 7 Aug 1995 → 10 Aug 1995 |
Conference
| Conference | 7th International Symposium on Environmental Degradation of Materials in Nuclear Power Systems |
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| Country/Territory | United States |
| City | Breckenridge |
| Period | 7/08/95 → 10/08/95 |